HashTable Class

Overview

• Key-value pair based collection.
• Contains DictionaryEntry objects.
• Not accessible by index, only by key.
• Values are returned based on the hash value when doing a foreach.
• Internally uses hashes to store objects, derived from the GetHashCode method on each object.
  • Hashes are used for equality of objects.
  • No duplicate hashes can occur.

Good practice

• When possible, use a generic collection instead of the object-based HashTable.
• Implement GetHashCode and Equals in custom objects when you need HashTable to treat objects as the same.
• Use a ListDictionary or HybridDictionary when working with smaller collections than 10 or unknown size collections.

Examples

Adding and Removing Elements

Hashtable a = new Hashtable();
a.Add("Key1", "Hello");
a.Add("Key2", "World");
a.Add("Key0", "Start");
Console.WriteLine(a["Key1"] + " " + a["Key2"]);
foreach (DictionaryEntry d in a) { Console.WriteLine(d.Value); }
foreach (var v in a.Values) { Console.WriteLine(v); }
 
a.Remove("Key1");
foreach (var k in a.Keys) { Console.WriteLine(a[k]); }